Chair lifts, gondolas, tramways, and the like all employ an endless cable supported for movement over a multiplicity of pulleys, which in turn are supported from towers. One of the most serious safety hazards in connection with such cable-based conveying systems is the possibility that the cable will become derailed from the various pulleys or sheaves and cause the chair, gondola, tram, etc. to fall to the ground with resultant injury to passengers.
While most cable-based conveying systems have cable catcher structures, it is important to be able to terminate or shut down the cable drive mechanism immediately in the event of derailment of the cable from the pulley assemblies. One approach to this problem is shown in my prior U.S. Pat. No. 3,822,369 in which a frangible cable sensing device is placed proximate a pulley assembly in a position at which a derailed cable would cause rupture of the sensor and accordingly automatic shut down of the cable drive apparatus.
Another approach to this problem is shown in my U.S. Pat. No. 4,019,002 in which relatively low inertia movable portions of the pulley assembly are biased by spring means for movement in the event of derailment of the cable. The apparatus further includes means for sensing movement of the low inertia portion of the pulley assembly. Upon derailment of the cable from the pulley assembly, the low inertia pulley mounting elements pivot and this pivotal motion is sensed and used to shut down operation of the pulley drive apparatus.
While the apparatus of my U.S. Pat. No. 4,019,002 had many advantages over the frangible sensor approach of my earlier patent, that part of the sensing apparatus which was responsive to movement of the low inertia portion of the pulley assembly had certain inherent disadvantages. My prior system employed elongated tendons which were mounted over pulleys or spools to transmit motion to a central sensing switch. Under some conditions, the tendon support pulleys could become frozen or require protective coverings to shield the same from ice. Additionally, my prior system had a certain inherent complexity of components which added to manufacturing, installation and adjustment costs.
Accordingly, it is an object of the present invention to provide a cable derailment shut down apparatus which may be used for terminating the operation of drive means for a moving cable and which has improved reliability of operation.
Another object of the present invention is to provide a cable derailment responsive apparatus that has a minimum number of components and may be readily adapted for use with existing cable conveying systems.
Still a further object of the present invention is to provide a cable derailment responsive apparatus which can be used to terminate the operation of drive means for a moving cable that is vibration and fatigue resistant, is not influenced by adverse weather conditions, and is easy to monitor and maintain.
The cable derailment responsive apparatus of the present invention has other objects and features of advantage, some of which will be set forth in more detail in or will become apparent from the following description of the preferred embodiment and the accompanying drawing.